An NHS hospital is being sued by a family who say doctors placed a "do not resuscitate" order on their relative, denying him potentially life-saving treatment, because he has Down's syndrome.

The unnamed family are bringing a legal challenge against a hospital in Kent where a doctor apparently decided staff should make no attempt to resuscitate the patient if he suffered cardiac or respiratory arrest, on the basis of his disability.

Lawyers for the family said a form added to the man's medical notes last September gave the reasons for no resuscitation as "Down's syndrome", "unable to swallow" (the man has a feeding tube in his stomach), "bedbound" and "learning difficulties".

The form, which said the decision should remain in force indefinitely, showed the doctor concerned had no discussion with the patient because the patient did not have mental capacity, said the lawyers.

The man, referred to as AWA, is still alive and in residential care a year later, after his carers argued for the DNR to be removed.

No information was given to his next of kin or sought from them, because they were "unavailable". A space where clinicians should report whether an information leaflet about such decisions has been given to AWA's family was blank.

Subsequent inquiries revealed that another DNR had been issued on the same patient, who also has dementia, a month earlier.

A close relative, X, who is also the man's "litigation friend", told the Guardian AWA's treatment had been "degrading and disgraceful".

East Kent Hospitals University NHS Foundation Trust said it could not comment on the case for legal reasons, but said it had "put a great deal in place in recent years to meet the needs of vulnerable patients" and had signed up to the Mencap charity's "Getting it right" charter on helping those with learning disability. It had a "clear and robust policy" on decisions not to attempt resuscitation which complied with professional guidance, it said.

News of the legal action comes two months before the high court in London conducts a judicial review of the actions of Addenbrooke's hospital, Cambridge, and health ministers over DNRs in a case brought by David Tracey, whose wife, Janet, died at Addenbrooke's.

Both the hospital and health department deny breaches of the Human Rights Act. There is no national government policy in England on DNRs, although hospitals should have local ones.

Sensitive life and death decisions of a different kind have been raised by cases brought by two severely disabled people with locked-in syndrome, Tony Nicklinson and a man known as Martin. Last month they lost a high court battle for permission to die with medical help.

X said AWA had gone into residential care in late 2010 after being cared for by his parents for nearly 50 years. In August 2011 he was admitted to Queen Elizabeth the Queen Mother hospital in Margate to have a feeding tube fitted. He returned there in September after problems with the tube.

After he was discharged, a carer unpacking his bag found a DNR form. "It was folded in four in his belongings. She was absolutely horrified. The issue had not been discussed with any relatives at the hospital," X said.

The home alerted AWA's community learning disabilities nurse, who telephoned the hospital and challenged the doctor. "Basically the doctor stated that with Down's syndrome at his age, people's reserve is limited, that they age faster than the rest of the population and have associated heart problems".

AWA had been admitted to hospital again, this time to Kent and Canterbury hospital, with pneumonia, and the nurse had to talk to a trust executive before the DNR form was removed, X said. "I was very angry and was ready to storm into the hospital. It is just not acceptable, not being consulted on whether someone lives or dies."

AWA was unaware of the DNR or the legal case, X said, but "a year on, he is sitting up in his chair and getting the best possible care … he seems well in himself".

Merry Varney, of the law firm Leigh Day & Co, representing X, said the case was one of most extreme it had seen. "To use Down's syndrome and learning difficulties as a reason to withhold lifesaving treatment is nothing short of blatant discrimination," she said.

"If an individual was physically preventing a doctor from administering life-saving treatment to a disabled relative, it would undoubtedly be a matter for police, yet we see doctors taking this decision without consent or consultation regularly. The absurdity of this is highlighted by the strict rules preventing patients such as Tony Nicklinson and our own case of Martin, people with capacity trying to make decisions to end their own life."

Varney added: "Having applied for and received AWA's medical notes, an earlier DNR appears to have been imposed, which we understand the family also had no knowledge of. Families and carers of those lacking mental capacity want to and have a right to be involved in decisions affecting access to medical treatment, yet both DNRs record that no family member or next of kin was consulted or informed."

Whose decision?

Behind the stark initials scattered through documents across the NHS and medical lawyers' officers – DNACPR (do not attempt cardio-pulmonary resuscitation), DNAR (do not attempt resuscitation), DNR (do not resuscitate) – lies a fraught debate over life and death choices.

Any decision not to attempt resuscitation legally rests with doctors, according to their regulator, the General Medical Council. They have no obligation to prolong life if they do not think it to patients' benefit.

Professional guidance from the British Medical Association, Resuscitation Council and Royal College of Nursing says for patients with mental capacity there should also be sensitive exploration of the "patient's wishes, feelings, beliefs and values". But a discussion should not be forced on them. Doctors' leaders also say good practice mean that, with patients' permission, such decisions should involve families.

If a patient lacks capacity, any previously expressed wishes should be considered,says the guidance. There should also be be discussion and agreement between the healthcare team and those close to or representing the patient.

If they have a welfare attorney or guardian, this person must be consulted about CPR decisions."Where a patient has not appointed a welfare attorney or made an advance decision, the treatment decision rests with the most senior clinician in charge of the patient's care.

"The views of those close to the patient should be sought, unless this is impossible, to determine any previously expressed wishes and what level or chance of recovery the patient would be likely to consider of benefit, given the inherent risks and adverse effects of CPR."

In England and Wales, "the Mental Capacity Act requires that best-interests decisions must include seeking the views of anyone named by the patient as someone to be consulted, anyone engaged in caring for the person or interested in the patient's welfare," says the guidance.

In England, unlike Scotland, there is no national NHS policy. It is left to local trusts.

• This article was amended on 13 September to add an additional element that was missing due to an error in the production process